1. Field of the Invention
The present invention relates to a data recording method for a memory card in which data such as picture data or character data may be stored, and a memory card system using the same. More particularly, the present invention is concerned with a method of recording data in a memory card having an EEPROM (Electrically Erasable Programmable Read Only Memory), and a memory card system using such a method.
2. Description of the Related Art
Today, a memory card using a semiconductor memory is predominant over a disket as means for recording data such as picture data generated by an electronic still camera or character data generated by a word processor, because the former is far smaller in size than the latter. It has been customary with a memory card for such an application to implement the semiconductor memory as an SRAM (Static Random Access Memory) which promotes rapid data reading and writing operations. However, because an SRAM is a volatile semiconductor memory, a memory card with an SRAM needs a back-up battery for preventing data from disappearing. Another problem is that an SRAM capable of storing a great amount of data such as picture data is expensive, increasing the overall cost of a memory card implemented thereby.
In light of the above discussion, a memory card with an EEPROM which is non-volatile and, therefore, does not need a back-up battery and is inexpensive is now under investigation. An EEPROM is capable of holding data therein for more than ten years without a battery. Some advanced EEPROMs are comparable with an SRAM in respect of the reading and writing rates and are less expensive (about one-fourth the cost of an SRAM). However, an EEPROM brings about other problems when it comes to the application to a memory card, as follows. With an EEPROM, it is necessary to give consideration to the processing for the erasure of data due to the nature of the device. Hence, a memory card with an EEPROM has to be provided with extra pins, or the system using such a memory card needs a special implementation. For this reason, a memory card with EEPROMs is not readily compatible with a conventional memory card with an SRAM. Specifically, data stored in an EEPROM cannot be rewritten by overwriting, i.e., such data has to be erased and then replaced with new data. Therefore, a memory card with an EEPROM needs extra pins for erasure which are not necessary is a memory card with an SRAM.
EEPROMs are generally classified into two types, i.e., an EEPROM of the type which erases all the data at one time and an EEPROM of the type erasing a predetermined block of data at a time. Although the block erasure type EEPROM can be dealt with in the same manner as an SRAM, it is more expensive than the collective erasure type EEPROM. On the other hand, the collective erasure or flushing type EEPROM cannot freely perform byte-by-byte data rewriting and, therefore, needs a special consideration in the aspect of use.
Furthermore, with an EEPROM, the total number of times that data can be erased and written is limited, e.g., from about 100 times to 10,000 times. Especially, the service life of the above-mentioned block erasure type EEPROM is noticeably reduced when repetitive writing concentrates in a particular location thereof.